For several ten years, the field effect transistor (FET) has been significantly developed in the application of semiconductor device. Due to its low-power dissipation and highly integrated technique, it plays the most important role in the field of very-large-scale integration (VLSI), particularly in ultra-large-scale integration (ULSI). There are many kinds of FET design, in which the main differences are in the gate and channel structures. In the fabrication of an integrated circuit using silicon as a material, a metal oxide semiconductor FET (MOSFET) has the properties of high yield rate and excellent reliability in addition to the above-described advantages of FET. Therefore, MOSFET has become the commonly used device in recent years. Certainly, there are some other designs for FET, such as a metal-insulator-semiconductor (MOSFET), an insulator-gate FET (IGFET), a junction-gate FET (JFET) using reversely biased p-n junction as a gate, a metal-semiconductor FET (MOSFET) using the metal-semiconductor schottky contact as a gate, and a modulation-doped FET (MOSFET).
In the fabrication of an integrated circuit using a GaAs material, although the electron mobility of GaAs is several times higher than that of silicon, the former is not so popular as the latter when used in the semiconductor industry. Except for its relatively expensive cost, the reason is that GaAs is unstable at a temperature greater than 650.degree. C. so that a high-quality oxide layer can not be fabricated in the high-temperature tube. The oxide layer with bad reliability and low interface density will bring about a difficulty in the fabrication of enhancement-mode MOS and limit the design and operation of many other FET structures. Therefore, it is desirable to overcome the problem encountered by the application of GaAs material.
In our previous studies (please see Hwei-Heng Wang et al., Japanese J. of Applied Physics, Pt. 2 (Letters) Vol. 37, No. 1 AB, pp. L-67-L70, 1998), we proposed a method for selectively forming an oxide layer on a portion uncovered by the photoresist or noble netal layer near the room temperature (40.about.70.degree. C.). Thus, how to combine the above-described processes for manufacturing the field effect transistors with this method and use GaAs as a substrate of metal oxide semiconductor FET (MOSFET) is the developing purpose of the invention.